linux-kernel - Re: [PATCH] ALSA: pcm: prevent UAF in snd_pcm

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Date:   Tue, 5 Dec 2017 09:19:32 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Kees Cook <keescook@...omium.org>,
        Robb Glasser <rglasser@...gle.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Markus Elfring <elfring@...rs.sourceforge.net>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        alsa-devel@...a-project.org, LKML <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] ALSA: pcm: prevent UAF in snd_pcm_info

+ stable

On Tue, Dec 5, 2017 at 9:16 AM, Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
> From: Robb Glasser <rglasser@...gle.com>
>
> When the device descriptor is closed, the `substream->runtime` pointer
> is freed. But another thread may be in the ioctl handler, case
> SNDRV_CTL_IOCTL_PCM_INFO. This case calls snd_pcm_info_user() which
> calls snd_pcm_info() which accesses the now freed `substream->runtime`.
>
> Signed-off-by: Robb Glasser <rglasser@...gle.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
>  sound/core/pcm.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/sound/core/pcm.c b/sound/core/pcm.c
> index 9070f277f8db..09ee8c6b9f75 100644
> --- a/sound/core/pcm.c
> +++ b/sound/core/pcm.c
> @@ -153,7 +153,9 @@ static int snd_pcm_control_ioctl(struct snd_card *card,
>                                 err = -ENXIO;
>                                 goto _error;
>                         }
> +                       mutex_lock(&pcm->open_mutex);
>                         err = snd_pcm_info_user(substream, info);
> +                       mutex_unlock(&pcm->open_mutex);
>                 _error:
>                         mutex_unlock(&register_mutex);
>                         return err;
> --
> 2.15.0.531.g2ccb3012c9-goog
>



-- 
Thanks,
~Nick Desaulniers